1. Field of the Invention
The present invention relates to a method of processing a wafer which is carried out as a pre-treatment of a wafer, such as a semiconductor wafer, in cutting and splitting the wafer into a plurality of individual devices such as semiconductor chips.
2. Description of the Related Art
As one of semiconductor chip mounting means, there has generally been used the mode of wire bonding in which an electrode pad and a lead frame, in a semiconductor chip joined to the lead frame, are connected to each other through metallic wires. However, reductions in size and thickness of electronic apparatuses using the semiconductor chips have been demanded more and more in recent years, and, in order to meet the demand, flip chips and the like have been developed and put to practical use. The flip chip pertains to the technology in which a plurality of projected electrodes called bumps having a height of about 15 to 100 μm, for example, are formed on the surface of the semiconductor chip, and the bumps are joined directly to electrodes present on the mounting substrate side. In some cases of the flip chip, an underfill material is placed between the electrodes on the wafer surface prior to splitting the wafer, for the purpose of preventing short-circuiting from occurring between the electrodes (refer to Japanese Patent Laid-open No. 2002-033342 and JP-A-2005-538572). As the underfill material, insulating resins such as epoxy and polyimide resins are used favorably.
In the recent semiconductor device technology, an insulation layer called “low-k” has been adopted for forming a wiring layer on the chip surface. The insulation layer is provided for lowering the permittivity to thereby smoothen the flow of electrical signals. However, when dicing in which a wafer is cut by a rotary blade containing diamond abrasive grains is conducted in splitting the wafer into a multiplicity of discrete chips, the insulation layer would be exfoliated or crushed because of its brittleness. In view of this, practically, only the insulation layer is first cut by a cutting method free of exertion of physical stresses, such as by irradiation with a laser beam, and thereafter the main body part (formed principally of single crystal silicon) of the wafer is cut by dicing or by irradiation with a laser beam.
Meanwhile, when a wafer is cut by irradiation with a laser beam, the heated wafer material (the wafer itself or the insulation layer) may be transpired, and the transpired component(s) may be deposited on the wafer surface, causing troubles such as short-circuit. The transpired component(s) deposited on the wafer surface are called debris, and, in the case of a chip of the type in which wiring is conducted by the above-mentioned wire bonding method, the debris can be easily removed by forming a protective film on the wafer surface. More specifically, the debris can be removed by a method in which irradiation with a laser beam is conducted while permitting deposition of the debris on a protective film and then the protective film is peeled off.
However, in the case where the above-mentioned bumps are formed on the wafer surface, it has been difficult to form the protective film in a good state on the wafer surface. This is because the material ordinarily used for forming the protective film is a solution, such as a water-soluble resist, and its properties are unsuitable for covering the projected parts.